Electrochemical power generating system

ABSTRACT

An electrochemical power generating system has a base unit and a replaceable fuel unit. The base unit comprises controller for controlling operation of the pump. The fuel unit comprises a second housing releasably connectable to the first housing and a row of metal-air cells in the second housing electrically inter-connected together. Each cell includes a casing, a metal anode within the casing, an air cathode, a spacer between the cathode and anode for preventing the anode from contacting the cathode, an electrolyte intake port and an electrolyte discharge port in the casing for passage of electrolyte through the casing and between the anode and cathode. The fuel unit further comprises a manifold, an electrolyte reservoir, and a fluid line. The manifold has an intake port and a plurality of discharge ports in fluid communication with the electrolyte intake ports of the cells so that electrolyte flowing through the manifold is directed through the intake ports of the cells. The electrolyte reservoir and intake port of the manifold are operatively connectable with the electrolyte pump for fluid communication therewith so that the pump is able to pump electrolyte from the reservoir to the manifold. The fluid line operatively connects the discharge ports of the cells with the reservoir so that electrolyte discharged from the cells flows to the reservoir. The replaceable fuel unit is releasably attachable to the base unit so that the fuel unit can be quickly attached to and detached from the base unit.

This is a continuation-in-part of application Ser. No. 07/955,583, filedOct. 2, 1992.

BACKGROUND OF THE INVENTION

This invention relates to metal-air cells and, more particularly, toelectrochemical power generating systems using metal-air cells.

Metal-air cell batteries generally have several serially connectedmetal-air cells. Each cell has an anode made of a reactive metal such asaluminum or magnesium and an air cathode spaced from the anode. Asuitable electrolyte, such as an aqueous solution of KOH, NaOH or NaCl,electrochemically couples the anode and cathode to produce an electricalpotential and supply current to an electrical load. During theelectrochemical reaction, the anode is consumed. When the anodes areconsumed, the battery must be refueled with new anodes and freshelectrolyte. Such refueling generally requires draining of spentelectrolyte from the battery, adding new metal anodes one-by-one, andreplenishing the electrolyte. The refueling operation in prior artmetal-air batteries is time consuming and usually results in the machineor device powered by the battery being inoperative for an extendedperiod during refueling.

Another problem with prior metal-air cell batteries is that during anodeconsumption the distance between the anode and cathode increases causinga decrease in voltage, power output, and efficiency of the battery.

Another problem is degradation of the electrolyte solution. As thereaction in the cell proceeds, reaction products build up in theelectrolyte solution, and concentration of the electrolyte increases,both of which cause a decrease in performance of the cell.

Another problem with prior metal-air cell batteries is the length oftime it takes for the battery to become fully operational, i.e., todeliver full power. The temperature of the electrolyte circulatingthrough the battery must be relatively high (e.g., 150° F.) before thebattery can fully energize the load. A metal-air cell cannot delivermuch power at low temperatures and, consequently cannot generate muchheat. Thus, if the electrolyte is initially cold, it typically takesseveral minutes to heat the circulating electrolyte to a sufficientoperating temperature. Such a warm-up time is often a nuisance to theuser and renders such metal-air cell batteries impractical for manyapplications. Moreover, when the cell is disconnected from itselectrical load, the anode continues to be consumed at a low rate andthereby reduces the operating life of the cell.

SUMMARY OF THE INVENTION

Among the objects of the present invention may be noted the provision ofimproved metal-air cells and electrochemical power generating systemwhich overcomes disadvantages and deficiencies associated with prior artcells and systems; the provision of such a generating system whichmaintains a substantially constant distance between the anode andcathode during consumption of the anode; the provision of such metal-aircells and power generating system which can be quickly and easilyrefueled when the anodes are depleted or consumed; the provision of sucha power generating system which more rapidly delivers full power; andthe provision of such a generating system which discontinues or reducesanode consumption when the metal-air cells are disconnected from itselectrical load.

Generally, an electrochemical power generating system of the presentinvention includes a metal-air cell for a metal-air cell battery. Thecell comprises a flexible, collapsible pouch having first and secondopposed walls. At least one of the walls includes an air-permeable andelectrolyte-impermeable air cathode. The cell further comprises a metalanode within the pouch and surrounded thereby having a first reactionface opposing the cathode, a spacer between the cathode and the reactionface of the anode for preventing the anode from contacting the cathode,and electrolyte intake and discharge ports for the pouch for passage ofelectrolyte through the pouch and between the anode and cathode.

In another aspect of the present invention, a metal-air cell battery hasa row or stack of collapsible metal-air cells arranged in face-to-facerelationship and electrically inter-connected. Each cell includes aflexible, collapsible pouch, a metal anode within the casing and havinga reaction face, and an air cathode having an outer face and an innerface with the inner face opposing the reaction face. A spacer ispositioned between the inner face of the cathode and the reaction faceof the anode for preventing the anode from contacting the inner face ofthe cathode. The cell also includes an electrolyte intake port and anelectrolyte discharge port for passage of electrolyte through the casingand between the anode and cathode. The battery further comprisesapparatus for urging opposite ends of the row of collapsible cellstoward each other thereby to urge the anode and cathode of each celltoward each other so that the distance between the inner face of thecathode and the reaction face of the anode of each cell remainsgenerally constant during consumption of the anode.

In still another aspect of the present invention, an electrochemicalpower generating system has a first portion, including an electrolytepump and electronic controls for controlling operation of the pump, anda separable second portion. The second portion comprises a row ofmetal-air cells electrically inter-connected together. Each cellincludes a casing, a metal anode within the casing and having a reactionface, and an air cathode having an outer face and an inner face with theinner face opposing the reaction face. A spacer is positioned betweenthe inner face of the cathode and the reaction face of the anode forpreventing the anode from contacting the cathode. The casing is providedwith an electrolyte intake port and an electrolyte discharge port forpassage of electrolyte through the casing and between the anode andcathode. A manifold having an intake port and a plurality of dischargeports is in fluid communication with the electrolyte intake ports of thecells so that electrolyte flowing through the manifold is directedthrough the intake ports of the cells. The second portion also includesan electrolyte reservoir and a mechanism for operatively connecting thedischarge ports of the cells with the reservoir so that electrolytedischarged from the cells flows to the reservoir. The electrolytereservoir and intake port of the manifold is operatively connectablewith the electrolyte pump for fluid communication therewith so that thepump is able to draw electrolyte from the reservoir and force it intothe manifold. The second portion is releasably attachable to the firstportion so that the second portion can be quickly attached to anddetached from the first portion.

In yet another aspect of the present invention, an electrochemical powergenerating system comprises at least one metal-air cell, an electrolytereservoir, and electrolyte transport apparatus for drawing electrolytefrom the reservoir and moving it through the cell. A first sensor sensesan operating condition of the power generating system. The system alsoincludes a controller for selectively energizing the electrolytetransport apparatus as a function of the sensed operating conditionwhereby energizing the electrolyte transport apparatus causeselectrolyte to be drawn from the reservoir and transported to the cell.

In yet another aspect of the present invention, an electrochemical powergenerating system comprises a battery having at least one metal-air cellincluding a casing, a metal anode within the casing and having areaction face, and an air cathode having an outer face and an inner facewith the inner face opposing the reaction face. The system furthercomprises apparatus for applying a bias voltage to the battery duringperiods when the battery is not supplying current to a load thereby toinhibit anode depletion. The voltage is of like polarity and of apotential at least equal to that of the battery.

In yet another aspect of the present invention, an electrochemical powergenerating system for supplying power to an electrical load comprises aprimary battery. The battery has at least one metal-air cell including acasing, an anode within the casing and having a reaction face, an aircathode having an outer face and an inner face with the inner faceopposing the reaction face, an electrolyte intake port in the casing forpassage of electrolyte through the casing and between the anode andcathode, and an electrolyte discharge port in the casing. The powergenerating system further includes apparatus for heating electrolytewithin the battery when the temperature of the electrolyte is below apredetermined temperature.

Other advantages and features will be in part apparent and in partpointed out hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view of an electrochemical power generatingsystem of the present invention with portions broken away to show manyof the components of the system;

FIG. 2 is a section on line 2--2 of FIG. 1, showing an end view of thesecond portion with portions broken away to show the elements of one ofthe cells;

FIG. 3 is a section on line 3--3 of FIG. 2 showing one of the cells;

FIG. 4 is a rear elevational view of one of the cells of the powergenerating system of FIG. 1;

FIG. 5 is a view of one of the anodes of the power generating system ofFIG. 1;

FIG. 6 is an elevational view of the row of cells of the powergenerating system of FIG. 1 with opposite ends of the row of cells beingurged together;

FIG. 7 is an elevational view similar to FIG. 6 except the anodes havebeen consumed and the cells have been compressed;

FIG. 8 is a schematic diagram of an alternative embodiment of anelectrochemical power generating system of the present invention;

FIG. 9 is a flow chart showing operation of the microprocessor of thepower generating system of FIG. 8;

FIG. 10 is a battery power versus time chart of the metal-air cellbattery of the power generating system of FIG. 8 as elect iyte i pulsedthrough the cells;

FIG. 11 is a cell temperature versus time chart of a metal-air cell ofthe power generating system of FIG. 8 as electrolyte is pulsed throughthe cell;

FIG. 12 is a schematic diagram of the power system in a deactivatedposition;

FIG. 13 is a schematic diagram of the power system during warm-up,immediately after being activated;

FIG. 14 is a schematic diagram of the power system during normaloperation;

FIG. 15 is a schematic diagram of the power system during initialshut-down, immediately after being deactivated;

FIG. 16 is a cross-sectional view of an alternative embodiment of ametal-air cell similar to the cell of FIG. 3 except the cell of FIG. 16has two cathodes;

FIG. 17 is a partial front elevational view of an alternative embodimentof a metal-air cell having an openable top;

FIG. 18 is a section view taken along line 18--18 of FIG. 17;

FIG. 19 is a top plan view of the metal-air cell of FIG. 17; and

FIG. 20 is an exploded perspective view of a cathode and wall of thepouch of the metal-air cell of FIG. 17.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIGS. 1-3, an electrochemical power generating system ofthe present invention, generally indicated at 20, is shown to have abase unit, constituting a first portion, generally indicated at 22, anda replaceable fuel unit, constituting a second portion, generallyindicated at 24. The base unit 22 includes a housing 26, an electrolytepump 28 within the housing 26, and a controller 30, constituting meansfor controlling operation of the pump 28. The fuel unit 24 comprises ahousing 32 and a row of metal-air cells 34 electrically interconnectedwithin housing 32. Each cell 34 includes a flexible pouch 36, a metalanode 38 within pouch 36, an air cathode 40, and spacers 42 forpreventing anode 38 from contacting cathode 40. Pouch 36 has anelectrolyte inlet port 44 and an electrolyte discharge port 46 forpassage of electrolyte through pouch 36 and between anode 38 and cathode40. A supply manifold 48 is within housing 32 for delivering electrolyteto the cells 34. The manifold 48 has an intake port 50 and a pluralityof discharge ports 52. The discharge ports 52 are in fluid communicationwith the inlet ports 44 of the cells 34 via a plurality of flexiblefluid lines 54 so that electrolyte flowing through manifold 48 isdirected through the inlet ports 44 of the cells 34. Also within housing32 is a discharge manifold 56 having a plurality of intake ports 58 anda discharge port 60. A plurality of flexible fluid lines 62 connectdischarge ports 46 of cells 34 to intake ports 58 of discharge manifold56. A conduit 64 connects discharge port 60 of discharge manifold 56 toan electrolyte reservoir 66 positioned below supply manifold 48.Electrolyte flows from cells 34, through discharge manifold 56, and theninto reservoir 66.

As shown in FIG. 1, a conduit 68 connects reservoir 66 to a heatexchanger 70 (preferably a fin and tube type heat exchanger) withinhousing 26. Pump 28 is connected to heat exchanger 70 via a conduit 71and to intake port 50 of supply manifold 48 via a conduit 72. Thus,reservoir 66 and intake port 50 of manifold 48 are operativelyconnectable with the electrolyte pump 28 for fluid communicationtherewith so that pump 28 is able to draw electrolyte from reservoir 66and force it into manifold 48. The electrolyte flows through cells 34and electrochemically couples anodes 38 and respective cathodes 40. Theflowing electrolyte also flushes reaction products from cells 34.Hydrogen gas generated by the reaction in cells 34 is carried todischarge manifold 56 by the electrolyte flowing through cells 34. Thehydrogen gas bubbles out of the electrolyte in discharge manifold 56 andis vented through a vent hole 67 in manifold 56. Preferably, reservoir66 is releasably connected to conduit 68 and conduit 72 is releasablyconnected to intake port 50 with quick-release fluid line connectors 74and 76, respectively. Connectors 74 and 76 releasably attach fuel unit24 to base unit 22 so that fuel unit 24 can be quickly attached to anddetached from base unit 22. When anodes 38 are consumed, fuel unit 24can be detached quickly from base unit 22 and replaced with a new secondunit. Thus, power generating system 20 can be rapidly refueled, therebyminimizing down time. The used fuel unit 24 can then be refueled orreclaimed.

As shown in FIGS. 3 and 4, cathode 40 has a substrate 78 and a currentcollector 80 attached to substrate 78. Substrate 78 has an outer face 82and an inner face 84. Substrate 78 is a sheet material (such as POREX®available from Porex Technology Corp. of Georgia) formed with orembedded with an activated carbonaceous material and is air-permeableand electrolyte-impermeable. Current collector 80 is a thin layer ofelectrically conductive material, such as nickel or stainless steel,formed on one of the faces of substrate 78. Preferably, currentcollector 80 comprises a printed circuit on one of the faces ofsubstrate 78 in a pattern having a dendritic web extending from a commonconductor 86. The printed circuit may be formed on substrate 78, forexample, by chemical etching, photo screening, or hot-foil stamping.

Pouch 36 is flexible and compressible and has first and second opposedwalls 88 and 90, preferably formed of a polymeric material, such aspolyethylene. The first wall 88 has a window opening 92 with the marginsof substrate 78 permanently sealed to first wall 88 all around windowopening 92. It is to be understood that window 92 may be a speciallytreated portion of wall 88. In either case, only the window area isactive and functions as a cathode. The exposed region of substrate 78,i.e., the portion of substrate 78 encompassed by window opening 92, isthe portion of substrate 78 which performs the cathodic function.Preferably, the margins of substrate 78 are bonded to first wall 88 byan appropriate adhesive. Alternatively, substrate 78 could be secured tofirst wall 88 by heat sealing. Preferably, the carbonaceous material isdeposited only in the interior region of substrate 78 with the marginsof substrate 78 being relatively free of such material. Having no (orlittle) carbonaceous material at the margins of substrate 78 enhancessecurement of substrate 78 to first wall 88. Substrate 78 may also beformed of fibrillated polyolefin having a sufficient amount ofcarbonaceous material in the interior region to provide the desiredelectrolytic reactions and having a reduced amount of carbonaceousmaterial (or none at all) at the margins to enhance securement to firstwall 88. The ratio of carbonaceous material to fibrillated polyolefinmay increase gradually from the edges of substrate 78 to the center ormay increase in an abrupt step. Alternatively, or additionally, themargins of substrate 78 may be impregnated with a substance (such aspolyethylene in solution) which promotes bonding to first wall 88.

Referring to FIGS. 3 and 5, anode 38 is a generally flat plate ofaluminum, aluminum alloy, or other suitable metal such as magnesium,having a first face, constituting a reaction face 94, and a second face96. The reaction face 94 opposes the inner face 84 of the cathode 40. Anelectrically conductive raised dendritic pattern 98 is on second face 96and extends from a common conductor 100. The dendritic pattern 98 ofanode 38 comprises a tapering main stem 98a that starts at the commonterminal conductor 100 and extends substantially across the second face96 and a plurality of tapering branches 98b extending from main stem98a. During operation of power generating system 20, anode 38 isconsumed from its reaction face 94 toward its second face 96. If theanode is not consumed uniformly along the reaction face or if thethickness of the anode is not uniform (i.e., if there are thin spots),breaks or openings can form in the anode before it is substantiallyconsumed. These breaks can isolate portions of the anode from theconductor, resulting in a partial or total reduction of energy outputfrom the cell. To prevent isolation of these portions from theconductor, the dendritic pattern 98 protrudes from second face 96. Evenif breaks or openings form in anode 38, dendritic pattern 98 keeps allportions of anode 38 in electrical contact with conductor 100. Thus,pattern 98 provides structural integrity and electrical communicationacross anode 38 to conductor 100 as the metal in anode 38 is consumed.Preferably, anode 38, including dendritic pattern 98, is formed from asingle homogeneous piece of metal.

Spacers 42 are positioned between cathode 40 and the reaction face 94 ofanode 38 to physically isolate anode 38 from cathode 40 by apredetermined spacing, typically on the order of about 3 mm. Spacers 42may be nubs or bosses integral with substrate 78 and projecting from theinner face 84 of substrate 78. Alternatively, anode-cathode spacing maybe maintained by a non-conducting lattice of criss-crossing members asdescribed in co-pending application Ser. No. 07/955,583, incorporatedherein in its entirety.

Referring to FIGS. 6 and 7, the entire row of cells 34 is preferablysurrounded by a resilient harness having banding straps 102 and tensionsprings 104 (only one of which is shown). The straps 102 extend aroundopposite ends of the row of cells 34 and are connected together bysprings 104. Although not shown, it is to be understood that the harnessis electrically insulated from terminal connectors 100 and 86. Springs104 are tensioned to urge opposite ends of the row of cells 34 towardeach other. Since pouch 36 of each cell 34 is flexible, the harnessurges the anode 38 and cathode 40 of each cell 34 toward each other withspacers 42 (see FIG. 3) of each cell being squeezed by the reaction face94 of anode 38 and the inner face 84 of cathode 40. FIG. 6 shows the rowof cells 34 before anodes 38 have begun to be consumed and, therefore,cells 34 and their respective anodes are relatively thick. FIG. 7 showsthe row of cells 34 with most of each anode being consumed and,therefore, cells 34 and their respective anodes are relatively thin andthe row of cells 34 is compressed. Preferably, fluid lines 54 and 62 areflexible to accommodate contraction or compression of the row of cells34. Alternatively, the intake and discharge manifolds could each have abellows-type configuration which contracts as the row of cells 34contracts. Since anode 38 and cathode 40 are being squeezed againstspacer 42, the distance between the inner face 84 of cathode 40 and thereaction face 94 of anode 38 remains substantially constant (i.e., thesame as the thickness of spacers 42) during consumption of anode 38.Since the distance between cathode 40 and reaction face 94 remainssubstantially constant, consumption of anode 40 does not result in adecrease in voltage and power output of the cell. Also, this distanceremains substantially constant during consumption of anode 38 regardlessof the initial thickness of anode 38. With thicker anodes, the metal-aircell battery is operable for longer periods between refueling andwithout an appreciable reduction in power output.

Although harness 103 constitutes the preferred means for urging theanode and cathode of each cell toward each other, it is to be understoodthat other means may be employed without departing from the scope ofthis invention. Examples of other ways of urging opposite ends of therow of cells 34 together include: tensioned elastomeric bands placedaround the row of cells; interacting wedges at ends of the row of cellswhich produce a compressive force against the ends; two rigid end platesengaging opposite ends of the row of cells with the end plates beingurged toward each other by tensioned springs; compression springs at oneend of the row of cells which urge the one end toward the other end; aninflatable bag at one end of the row of cells which, upon inflation,urges the one end toward the other end; or a hydraulic cylinder at oneend of the row of cells which, upon being pressurized, urges the one endtoward the other end.

Referring again to FIG. 1, the base unit 22 further includes an air pump108, constituting a depolarization air system, for forcing slightlycompressed air across the cathodes. A plurality of inter-cell spacers orseparators 106 (also shown in FIGS. 2, 3 and 6), preferably formed of asynthetic resin, are interposed between adjacent cells 34 to provide airspaces adjacent the cathodes so that the depolarizing air can circulatearound the cells and to the cathodes. The circulation of air aroundcells 34 also helps to cool the cells. The thickness of the spacers 106between cells 34 may vary so that the sizes of the spaces betweenadjacent cells varies to achieve variable cooling of the cells. Forexample the inter-cell spacing can decrease from one end of the row ofcells to the other, or the inter-cell spacing can decrease from thecenter of the row of cells toward the ends of the row. The thickness ofspacers 106 is selected generally to achieve equalization of thetemperatures of the cells 34 in the row of cells.

A cooling fan 110 is within housing 26 for forcing cooling air acrossthe fins of heat exchanger 70 to cool electrolyte within heat exchanger70. A lead-acid battery 112, or other suitable secondary battery,operates pump 28, controller 30, and pump 108 and fan 110 duringstart-up of the metal-air cell battery.

Referring to FIGS. 1, 4 and 6, the conductors 86 of cathodes 40 aredirectly connected to the conductors 100 of anodes 38 of adjacent cellsthereby connecting cells 34 in series to each other. Battery stack endcathode conductor 86 is connected to negative contact pad 115a via anelectric cable (not shown). Battery stack end anode conductor 100 isconnected to positive contact pad 115b via electric cable 113b. Positiveand negative electrical contact pads 115a and 115b (see FIG. 2) extendthrough a side wall 114 of housing 32. The contact pads 115a and 115bare interengageable with two like polarity contact pads (not shown)extending through a side wall 116 of housing 26 for electricallyconnecting the metal-air cell battery to an external load and tolead-acid battery 112. Base unit 22 further includes positive andnegative load engageable terminals (not shown) through a second sidewall 118 of housing 26 and suitable conductors (not shown) for providingelectrical energy to the terminals.

Another embodiment of an electrochemical power generating system of thepresent invention, generally indicated at 220, is shown schematically inFIG. 8. Power generating system 220 comprises a fluid system, a gassystem, and an electrical system. The fluid system includes a sump 224,an electrolyte filter 226, a heat exchanger 228, and a reversible-flowpump 230 for moving electrolyte through a plurality of metal-air cells,generally indicated at 222. Electrolyte flows from cells 222 through aconduit 232 and to sump 224 which includes a plurality of baffles 224afor collection of reaction products discharged from the cells.Electrolyte from sump 224 flows through a conduit 234 to filter 226,which filters reactants, generated in cells 222, from the electrolyte.Electrolyte moves from filter 226 to heat exchanger 228 via a conduit236. Heat exchanger 228 is preferably a fin and tube type heat exchangerand includes a cooling fan 229 for moving air across the fins forcooling the electrolyte when the electrolyte exceeds a predeterminedtemperature. Heat exchanger 228 is in fluid communication with pump 230via a conduit 238. An electrolyte reservoir 240 is in fluidcommunication with conduit 238 via a conduit 242. Electrolyte fromreservoir 240 is introduced into the circulatory system only if and whenthe electrolyte in sump 224 falls below a minimum acceptable level. Thereservoir 240 maintains proper electrolyte level in cells 222.Electrolyte from pump 230 flows through a conduit 244 to cells 222 via aconcentration sensor 250. The electrolyte may be an aqueous solution ofpotassium hydroxide (KOH), sodium hydroxide (NaOH), sodium chloride(NaCl), or any other suitable electrolyte. The electrolyte in sump 224maybe seeded with micro-crystals of the anticipated reaction products,such as Al(OH)₃ in aluminum air cells where the electrolyte is KOH, tocause the reaction products to precipitate out of the electrolytesolution and facilitate the trapping of these products in sump 224.

Power generating system 220 also includes an electrolyte concentratereservoir 246, a solenoid-actuated metering valve 248, and anelectrolyte concentration sensor 250. Concentrate reservoir 246 is incommunication with conduit 244 via two conduits 252 and 254 and valve248. Sensor 250 senses concentration of electrolyte and may be, forexample, a conductivity sensor which measures the conductivity of theelectrolyte solution to gauge the electrolyte concentration.Alternatively, sensor 250 may be a pH sensor which measures the pH ofthe electrolyte solution to gauge the electrolyte concentration. Whenthe concentration of the electrolyte falls below a predetermined value,valve 248 meters concentrated electrolyte from reservoir 246 to conduit244. The concentrated electrolyte increases the concentration ofelectrolyte transported to cells 222. Thus, weak electrolyte isautomatically replenished.

An air pump 256 forces depolarizing air to cells 222. The circulatingair is passed through a filter 257 to remove contaminants, particularlycarbon particles, that might contaminate the system. The electrochemicalreaction in the cells produces hydrogen gas which is vented from thecells by a conduit 258. Conduit 258 communicates with a catalytic bed260. Air and byproduct gasses, such as hydrogen, from cells 222 areforced to pass through catalytic bed 260 where the hydrogen isrecombined with atmospheric oxygen to form water. The water drains fromcatalytic bed 260 to sump 224 through a conduit 262, where itreplenishes moisture lost from the electrolyte during operation of cells222. Alternatively, or in addition, a vent can be provided to allow H₂gas to escape, with or without the assistance of air pump 256 or fan229.

Power generating system 220 has a controller 264 for controlling pump230, cooling fan 229, metering valve 248, and air pump 256. A lead-acidbattery 266 or any suitable supplemental battery operates controller 264and pump 230 during start-up of power generating system 220. Duringoperation of power generating system 220, i.e., when power is beingsupplied to a load, battery 266 serves as an accumulator foraccommodating power surges demanded by the load above the normal outputlimits of cells 222. Battery 266 is normally connected in parallel withthe row of cells 222 via controller-controlled switches 267 described inmore detail below. Lead-acid battery 266 provides power to activategenerating system 220, and to complete shut-down operations after amaster switch 269 is opened. A voltmeter 261 and ammeter 263 areprovided to give the operator an indication of the system voltage andthe amount of current being drawn as power generating system 220 isloaded. Power generating system 220 could also be provided with otherindicators, such as temperature indicators, electrolyte fluid levelindicators, and a fuel indicator indicating the thickness of the anodesor the operating time remaining.

Referring to FIG. 8 and the flow chart of FIG. 9, the operation of pump230 and fan 229 by controller 264 will be described. Controller 264enables cells 222 to rapidly reach full power even when the electrolyteis initially cold. A first temperature sensor 268 senses electrolytetemperature in the circulatory system. A second temperature sensor 270is in at least one of the cells for measuring the temperature ofelectrolyte in the cells. Initially, no electrolyte is in the cells ofbattery 222. When the power generating system 220 is turned on,controller 264, at step 272, compares the system temperature, asmeasured by first sensor 268, with a predetermined temperature T_(S). Ifthe system temperature does not exceed temperature T_(S), controller 264activates pump 230 for a brief predetermined duration D₁ at step 274.This brief activation causes a charge (volume) of electrolyte to bepumped into the cells. The electrolyte charge is held statically (ornear statically) within the cells so that it quickly absorbs heat fromthe electrochemical reaction taking place between the cathodes andanodes. In step 276, after the charge is pumped into the cells,controller 264 compares the electrolyte temperature in the cells, asmeasured by second sensor 270, with a predetermined temperature T₁. Ifthe cell temperature does not exceed temperature T₁, controller 264reexecutes step 276, and repeatedly does so until the cell temperatureexceeds temperature T₁. When temperature T₁ is exceeded, controller 264returns to start at step 278. If the system temperature does not exceedtemperature T_(S), controller 264 will repeat steps 272-278. As steps272-278 are repeated, a fresh charge of electrolyte is pumped into thecells and the old charge (i.e., the one heated during the previouscycle) is forced into sump 224. Controller 264 will repeat steps272-278, incrementally elevating the temperature in the fluid system(including reservoir 240), until the system temperature exceedstemperature T_(S). By pulsing charges of electrolyte into the cells andallowing them to remain static until they reach an optimal temperature,cells 222 can operate at near full power without waiting for all theelectrolyte in the system to heat up. Also, since cells 222 quicklyoperate at near full power, the system electrolyte is heated at a muchfaster rate than could be accomplished with a continuous flow system.Graphs representing battery power vs. time and cell temperature vs. timeduring electrolyte pulsing are shown in FIGS. 10 and 11.

Alternatively, if the system temperature is less than T_(S), then thepump 230 may be repeatedly turned on for a first predetermined period oftime t₁ (n seconds long) and turned off for a second predeterminedperiod of time t₂ (m seconds long) until the system temperature reachesT_(S). In particular, if the temperature of the electrolyte solution isnot greater than T_(S), then the controller turns pump 230 on for thefirst period of time t₁ sufficient to fill the cells with electrolyte,and then turns the pump off and waits the second predetermined period oftime t₂. The controller then determines whether the temperature of theelectrolyte solution in the cells (as sensed by a suitable temperaturesensor) is greater than a predetermined temperature T₁. If thetemperature of the electrolyte solution is not greater than T₁, then thecontroller turns the pump on for the predetermined period of time t₁ toexchange the electrolyte solution in the cells, and then turns the pumpoff, and again waits the second predetermined period of time t₂, beforethe cell temperature is again read. If the temperature of theelectrolyte solution is greater than T₁, then the controller determineswhether the system temperature has reached the temperature T_(S).

When controller 264 determines that the system temperature exceedstemperature T_(S), pump 230 is operated for continuous flow in step 280.In step 282, controller 264 compares the electrolyte temperature in thecells, as measured by second sensor 270, with a predeterminedtemperature T₃. If the cell temperature exceeds temperature T₃,controller 264, in step 284, energizes cooling fan 229 to coolelectrolyte passing through heat exchanger 228. If in step 282, the celltemperature does not exceed temperature T₃, controller 264 compares thecell temperature with a predetermined temperature T₂ (which is less thantemperature T₃) in step 286. If the cell temperature is lower thantemperature T₂, controller 264 signals a relay for deactivating coolingfan 229 in step 288. Controller 264 then returns to start in step 290.Temperatures T₂ and T₃ are selected to maintain a stable temperature forthe electrolyte solution within the optimum operating range of thesystem. Thus, controller 264 selectively energizes fan 229 forcontrolling cooling of the electrolyte.

Controller 264 controls metering valve 248 in response to electrolyteconcentration sensor 250, opening valve 248 to release concentratedelectrolyte into conduit 244 to boost the concentration of electrolytewhen sensor 250 detects that the concentration has fallen below apredetermined level. Controller 264 may further control pump 230 byvarying the pulse duration D₁ as a function of electrolyte temperature.For example, controller 264 could cause duration D₁ to increase as thesystem temperature increases. Also, controller 264 could control pump230 as a function of some operating condition of cells 222 other thanelectrolyte temperature. For example, pump 230 may be operated as afunction of a voltage generated by cells 222.

As noted above, controller 264 also controls operation of powergenerating system 220 during shut-down. When a master switch 269 ismanually set so that system 220 is deactivated, controller 264 initiallyconnects lead-acid battery 266 across the row of cells 222, applyingreverse polarity voltage to inhibit electron flow and thus help protectthe anodes in cells 222 from further electrochemical depletion. However,if system 220 is not turned on again within a predetermined duration D₂(e.g., one hour), then a timing switch within controller 264 disconnectsthe lead-acid battery 266 from cells 222 and sends a signal to causepump 230 to operate in reverse pump mode to draw electrolyte from thecells and force it back through heat exchanger 228 and into sump 224.After a predetermined duration, or when cells 222 are substantiallyempty, controller 264 deactivates pump 230.

The start up and shut down operations of system 220 are illustrated inFIGS. 12-15. In FIG. 12, system 220 is shown in a deactivated state,with no power being supplied to the load. In FIG. 13 the system is shownimmediately after switch 269 has been moved to the position shownthereby causing current from lead-acid battery 266 to be provided tocontroller 264, and causing a solenoid actuated master contactor 271 toconnect battery 266 to the load, switch 273, ganged to switch therebyconnects a first plurality 275 of cells 222 (constituting a first partof the row of cells 222) to a second plurality 277 of cells 222(constituting a second part of the row of cells 222) in series. In theposition shown, switch 269 also energizes a solenoid 279 thereby toreposition two switches 281 and 283. The repositioning of switch 281causes battery 266 to be connected to the row of cells 222 in series,and the repositioning of switch 283 causes battery 266 and the row ofcells 222 to be connected through a current-limiting resistor 285 toground. Thus, battery 266 provides a current, limited by resistor 285,to heat cells 222 and to depassivate the anodes, breaking up films (suchas an oxidation layer) that may form on the anodes. When cells 222 havebeen warmed, a normally closed thermal switch 287 opens, de-energizingsolenoid 279 and repositioning switches 281 and 283. As shown in FIG.14, when switch 281 is repositioned, it connects the negative terminalof the row of cells 222 to ground and switch 283 connects the positiveterminal of the row of cells to the load, in parallel with battery 266.Battery 266 and the row of cells can thus provide current to the load inparallel. However, the higher voltage output of the row of cells atmaximum rated current levels exceeds the voltage of battery 266, andthus the row of cells usually provides all of the power output and alsokeeps battery 266 charged.

When the system 220 is shut down by moving switch 269 to the positionshown in FIG. 15, master contactor 271 is de-energized, disconnectingthe output from the load. Switch 269 also initiates operation of acorrosion inhibit timer 289 which temporarily closes two normally openswitches 291 and 293, and repositions switch 273 separating firstplurality 275 of cells and second plurality 277. Closing switch 291connects battery 266 through a current-limiting resistor 295 to thepositive terminal of the first plurality 275 of cells, the negativeterminal of which is connected to ground. Closing switch 293 connectsthe negative terminal of the second plurality 277 of cells through acurrent-limiting resistor 297 to ground, the positive terminal of whichis already connected to battery 266. With switches 291 and 293 closed,battery 266 provides positive bias voltage to protect the anodes incells 222 from consumption. After a predetermined period, corrosioninhibit timer 289 sends a signal to controller 264 to open switches 291and 293. Controller 264 then activates pump 230 in reverse mode to drainthe electrolyte into sump 224, to prevent further consumption of theanodes.

Another embodiment of a metal-air cell, generally indicated at 334, isshown in FIG. 16. Cell 334 includes a flexible pouch 336, a metal anode338 within pouch 336, two air cathodes 340, and two spacers 342 forpreventing cathodes 340 from contacting anode 338. The primarydifference between cell 334 and cell 34 is that cell 334 has twocathodes. Each cathode 340 has a substrate 378 and a current collector380. Each substrate 378 is air-permeable and electrolyte-impermeable.Anode 336 has a first reaction face 394a opposing the inner face of onecathode and a second reaction face 394b opposing the inner face of theother cathode. Pouch 336 has first and second opposed walls 388 and 390,having first and second windows 392a and 392b, respectively. Spacers 342are electrolyte-resistant nonconductive fibrous sheets formed ofrandomly oriented fibers and preferably have a thickness ofapproximately 3 mm. Alternatively, spacers 342 may be knitted, woven,felted, etc., and may be formed of nylon, polyamide fusing web,polyester, etc. Having cathodes opposing both faces of anode 338 doublesthe reaction surface area and effectively doubles the power output ofcell 334.

Another embodiment of a metal-air cell, generally indicated at 400, isshown in FIGS. 17-20. Cell 400 comprises a flexible pouch 402 havingfirst and second walls (or panels) 404 and 406, the perimeters of whichare sealed together to form a pouch having an open top. First and secondpanels 404 and 406 are air-permeable and electrolyte-impermeable. Firstand second films 408 and 409 of cathodic material, such as an activatedcarbonaceous material, are deposited on or embedded in the innersurfaces of first and second panels 404 and 406, respectively, and firstand second current collectors 410 and 411 are secured to the innersurfaces in contact with films 408 and 409. Panels 404 and 406constitute substrates for films 408 and 409 and support currentcollectors 410 and 411. Panel 404, film 408, and current collector 410constitute a first air cathode 412 having an inner face 414; panel 406,film 409, and current collector 411 constitute a second air cathode 413having an inner face 415. Within pouch 402 is a metal anode 416, havingfirst and second reaction faces 418 and 420, and spacers 422 and 423.The first face 418 of anode 416 opposes inner face 414 of cathode 412and the second face 420 opposes inner face 415 of cathode 413. Spacer422 is between inner face 414 and first face 418 and spacer 423 isbetween inner face 415 and second face 420 for preventing anode 416 fromcontacting cathodes 412 and 413. Each current collector has a conductiverectangular frame 424 surrounding one of the films 408 or 409, anelectrical terminal connector 426 adjacent a corner of frame 424, and aplurality of conductive filaments 428 each extending from electricalconnector 426 to frame 424. As an alternative to the filaments, eachcurrent collector may have a grid pattern or any other suitable pattern.Connector 426 extends through pouch 402 at the sealed perimeter.

Pouch 402 includes an inlet 430 and an outlet 432 to allow electrolytesolution to be circulated through cell 400. Inlet 430 is preferablylocated generally adjacent the bottom of pouch 402 at the sealedperimeter, and outlet 432 is preferably located generally adjacent thetop of pouch 402 at the sealed perimeter to cause thorough circulationof the electrolyte solution from inlet 430, up and across cell 400, tooutlet 432. Elongate, resilient sealing beads 438 and 440 are fixedlysecured to panels 404 and 406, respectively. The beads 438 and 440 areadjacent to and extend along the opening at the top of pouch 402 and areengageable with each other to seal the top of the pouch. An elongateclamp 442 fits over beads 438 and 440 to releasably compress the beadstogether to close and seal pouch 402. An electrical terminal connector444 extends upwardly from anode 416 and between sealing beads 438 and440 and through a slot 446 at one end of clamp 442. Sealing beads 438and 440 are sufficiently yieldable to accommodate connector 444.Preferably, an end cap 447 is placed over the slotted end of clamp 442to secure the clamp on the pouch. Clamp 442 is easily removed from pouch402 to allow opening of the pouch to remove the remainder of the spentanode, and install a replacement anode. Clamp 442 and sealing beads 438and 440 constitute means for releasably closing the top of the pouch toseal against leakage of electrolyte therethrough.

Although cell 400 has been described as having two cathodes, it is to beunderstood that activated carbonaceous material may coat or be embeddedin the entire inner surface of the pouch and a current collector mayblanket the entire inner surface of the pouch so that the pouch,carbonaceous material and current collector form an active cathode whichenvelops the anode.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:
 1. An electrochemical power generating system havinga base unit and a replaceable fuel unit, said base unit comprising afirst housing, an electrolyte pump in the first housing, and acontroller for controlling operation of the pump, said fuel unitcomprising:a second housing releasably connectable to the first housing;a row of metal-air cells in the second housing electricallyinter-connected together, each cell including a casing, a metal anodewithin the casing and having a reaction face, an air cathode having anouter face and an inner face with the inner face opposing the reactionface, a spacer between the inner face of the cathode and the reactionface of the anode for preventing the anode from contacting the cathode,an electrolyte intake port and an electrolyte discharge port in thecasing for passage of electrolyte through the casing and between theanode and cathode; a manifold having an intake port and a plurality ofdischarge ports in fluid communication with the electrolyte intake portsof the cells so that electrolyte flowing through the manifold isdirected through the intake ports of the cells; an electrolytereservoir, said electrolyte reservoir and intake port of the manifoldbeing operatively connectable with the electrolyte pump for fluidcommunication therewith so that the pump is able to pump electrolytefrom the reservoir to the manifold; and at least one fluid line foroperatively connecting the discharge ports of the cells with thereservoir so that electrolyte discharged from the cells flows to thereservoir; said replaceable fuel unit being releasably attachable to thebase unit so that the fuel unit can be quickly attached to and detachedfrom the base unit.
 2. An electrochemical power generating system as setforth in claim 1 wherein the casing of each cell comprises a flexible,collapsible pouch and wherein the cells are arranged in face-to-facerelationship, said power generating system further comprising means forurging opposite ends of the row of cells toward each other so that thedistance between the inner face of the cathode and the reaction face ofthe anode of each cell remains generally constant during consumption ofthe anode.
 3. An electrochemical power generating system as set forth inclaim 2 wherein the means for urging opposite ends of the row of cellstoward each other comprises a resilient harness extending around the rowof cells.
 4. An electrochemical power generating system as set forth inclaim 3 further comprising a plurality of flexible conduits fordirecting electrolyte flowing through the manifold to the intake portsof the cells, each conduit having a first end connected to one of thedischarge ports of the manifold and a second end connected to one of theintake ports of the cells.
 5. An electrochemical power generating systemas set forth in claim 1 wherein the anode of each cell comprises agenerally flat plate having a first face, a second face, and a raiseddendritic pattern protruding from the second face for providingstructural integrity and electrical conduction across the plate, thefirst face of each anode comprising the first reaction face of suchanode.
 6. An electrochemical power generating system as set forth inclaim 1 further comprising a depolarization air system for feeding airto the cathode of each cell.
 7. An electrochemical power generatingsystem as set forth in claim 1 wherein the controller is in the firsthousing.
 8. An electrochemical power generating system as set forth inclaim 1 wherein the manifold and electrolyte reservoir are at leastpartially contained by the second housing.
 9. An electrochemical powergenerating system as set forth in claim 1 further comprising first andsecond fluid conduits operatively connected to the pump, andquick-release fluid line connectors for operatively connecting thereservoir and intake manifolds to the first and second fluid conduits,said quick-release fluid line connectors facilitating quick attachmentand detachment between the fuel unit and base unit.
 10. Anelectrochemical power generating system comprising:at least onemetal-air cell; an electrolyte reservoir; electrolyte transport meansincluding a pump for pumping electrolyte from the reservoir and movingit through the cell; a sensor for sensing an operating condition of thegenerating system; and a controller responsive to the sensor forselectively energizing the pump as a function of the sensed operatingcondition whereby energizing the pump causes electrolyte to betransported from the reservoir to the cell.
 11. An electrochemical powergenerating system as set forth in claim 10 wherein the sensor is atemperature sensor for sensing the temperature of electrolyte in thesystem.
 12. An electrochemical power generating system as set forth inclaim 11 wherein the controller energizes the pump when sensedelectrolyte temperature exceeds a temperature T₁.
 13. An electrochemicalpower generating system as set forth in claim 12 wherein the controlleris responsive to the temperature sensor for energizing the pump for abrief duration D₁ to pump a charge of electrolyte into the cell wherethe charge is held substantially statically in the cell until the sensedelectrolyte temperature exceeds the temperature T₁, whereupon the pumpis again energized by the controller for a duration D₁ to pump anothercharge of electrolyte into the cell.
 14. An electrochemical powergenerating system as set forth in claim 10 wherein the controller isadapted for energizing the pump for a duration D₁.
 15. Anelectrochemical power generating system as set forth in claim 14 whereinthe duration D₁ is a function of the sensed operating condition.
 16. Anelectrochemical power generating system as set forth in claim 10 furthercomprising means for cooling electrolyte, said controller being adaptedfor selectively energizing the electrolyte cooling means as a functionof the sensed operating condition whereby energizing the electrolytecooling means cools the electrolyte.
 17. An electrochemical powergenerating system as set forth in claim 16 wherein the controller isadapted for energizing the electrolyte cooling means when electrolyte inthe power generating system exceeds a temperature T₃, and fordeenergizing the electrolyte cooling means when the temperature of theelectrolyte is less than a temperature T₂.
 18. An electrochemical powergenerating system as set forth in claim 10 wherein the pump comprises areversible pump.
 19. An electrochemical power generating system as setforth in claim 10 wherein the electrolyte transport means furthercomprises at least one conduit for conveying electrolyte from the pumpto the cell.
 20. An electrochemical power generating system as set forthin claim 19 further comprising first conveying means for conveyingelectrolyte from the cell to one of the electrolyte transport means andthe electrolyte reservoir.
 21. An electrochemical power generatingsystem as set forth in claim 20 wherein said first conveying meansfurther comprises a sump for collecting reaction products dischargedfrom the cells.
 22. An electrochemical power generating system as setforth in claim 21 further comprising a catalytic converter forcatalyzing the conversion to water of hydrogen produced by the cell. 23.An electrochemical power generating system as set forth in claim 22further comprising second conveying means for conveying water from thecatalytic converter to the first conveying means.
 24. An electrochemicalpower generating system as set forth in claim 10 wherein said sensorcomprises a first temperature sensor for sensing the temperature ofelectrolyte in the system, said power generating system furthercomprising a second temperature sensor for sensing the temperature ofelectrolyte in the cell, the controller being responsive to said firstand second temperature sensors and capable of: (a) turning the pump onfor a first duration t₁ and turning the pump off for a second timeperiod t₂ ; (b) repeating (a) until the second temperature sensor sensesan electrolyte temperature of at least T₁.
 25. An electrochemical powergenerating system as set forth in claim 24 wherein the controller isfurther capable of repeating (a) and (b) until the first temperaturesensor senses an electrolyte temperature of at least T_(S) and thenturning the pump on to run continuously.
 26. An electrochemical powergenerating system as set forth in claim 10 wherein said sensor comprisesa first temperature sensor for sensing the temperature of electrolyte inthe electrolyte transport means, said power generating system furthercomprising a second temperature sensor for sensing the temperature ofelectrolyte in the cell, the controller being responsive to the firstand second temperature sensors for (a) energizing the pump for a briefduration D₁ when the first temperature sensor senses an electrolytetemperature less than a temperature T_(S) to pump a charge ofelectrolyte into the cell where the charge is held substantiallystatically in the cell until the second temperature sensor senses anelectrolyte temperature in excess of the temperature T₁ and (b)energizing the pump continuously when the first temperature sensorsenses an electrolyte temperature in excess of the temperature T_(S).27. An electrochemical power generating system comprising:a batteryhaving at least one metal-air cell including a casing, a metal anodewithin the casing and having a reaction face, and an air cathode havingan outer face and an inner face with the inner face opposing thereaction face; and a controller for causing a bias voltage to be appliedto the battery during periods when the battery is not supplying currentto a load thereby to inhibit anode depletion, and for causing removal ofthe bias voltage from the battery after the bias voltage has beenapplied to the battery for a duration D₂ ; said bias voltage being oflike polarity and of a potential at least equal to that of the battery.28. An electrochemical power generating system as set forth in claim 27wherein the source of the bias voltage is a secondary battery.
 29. Anelectrochemical power generating system for supplying power to anelectrical load comprising:a primary battery having at least onemetal-air cell including a casing, an anode within the casing and havinga reaction face, an air cathode having an outer face and an inner facewith the inner face opposing the reaction face, an electrolyte intakeport in the casing for passage of electrolyte through the casing andbetween the anode and cathode, and an electrolyte discharge port in thecasing; and means for heating electrolyte within the battery when thetemperature of the electrolyte is below a minimum temperature.
 30. Anelectrochemical power generating system as set forth in claim 29 whereinsaid heating means comprises a supplemental power source connected inseries with the primary battery for selectively carrying the loadwhereby current from the supplemental power source passes through theprimary battery to heat the electrolyte.
 31. An electrochemical powergenerating system as set forth in claim 30 further comprising acontroller for operatively connecting the primary battery andsupplemental power source in series when the temperature of theelectrolyte is below the minimum temperature and for operativelyconnecting the battery and supplemental power source in parallel whenthe temperature is above the minimum temperature.
 32. An electrochemicalpower generating system as set forth in claim 31 further comprising asensor for sensing electrolyte temperature within the primary battery,said controller being responsive to the sensor.
 33. An electrochemicalpower generating system as set forth in claim 32 wherein thesupplemental power source comprises a secondary battery.
 34. Anelectrochemical power generating system comprising:a battery having atleast one metal-air cell including a casing, a metal anode within thecasing and having a reaction face, an air cathode having an outer faceand an inner face with the inner face opposing the reaction face, anelectrolyte intake port and an electrolyte discharge port in the casingfor passage of electrolyte through the casing and between the anode andcathode; and a controller for causing a bias voltage to be applied tothe battery during periods when the battery is not supplying current toa load thereby to inhibit anode depletion, and for causing emptying ofelectrolyte from the casing of the cell after the bias voltage has beenapplied to the battery for a duration D₂ ; said bias voltage being oflike polarity and of a potential at least equal to that of the battery.